It is known that, particularly when certain fluxes are used, the porosity of the joint between a battery lug and its cast-on strap can be considerably reduced if the temperature of the lug is raised significantly and preferably to over 150.degree. C. The heating normally takes place using hot air and the air temperature is typically 350.degree.-400.degree. C. For the most part this method has been limited to certain specialized batteries, such as computer stand-by batteries, because the hot air from the nozzle tends to degrade the separators which are used between the plates in most common form of batteries, e.g. automotive or truck batteries.
Where the separators are individual sheets between the plates at least one manufacturer has attempted to push physically the separators away from the hot air stream but without any significant success. Such an approach is in any case impractical when, as is quite common, the separators are in the form of an envelope in which the battery plates sit.